A photo guest book - polaroid and washi tape! Get a cheap but cute polaroid camera, a blank notebook, and washi tape in your chosen colors. Have guests take photos and then leave a message underneath. Love this, but polaroid film is expensive and rare!
Flower girl delivers a message to the groom from the bride when she comes down the aisle. LOVE that idea. Totally doing that. Maybe change the message so it doesn't seem like the flower girl wants to kiss the groom.
Wedding Favor Idea - A Hangover Helper Kit! Yes, go ahead and LOL (I sure did!), but don't you just love the idea of sending your guests out with a "hangover helper" kit? Sounds like a must-have for all the full-throttle wedding party animals.
Another DIY wedding decor idea that is cheap and so pretty just fill mason jars with baby's breath or inexpensive flowers and line the aisle with them hanging off the chairs. I love the burlap and twine on the jar too.